1. Field of the Invention
This invention relates to an electrophotographic copying apparatus of the slit exposure type using a movable original carriage or optical system, and more particularly to an electrophotographic copying apparatus provided with a novel control system.
2. Description of the Prior Art
Copying apparatus have heretofore employed a photosensitive medium in the form of a drum or a belt or the like which may be reused. However, the photosensitive medium presents different sensitivity characteristics depending on its history of irradiation with light, and accordingly the sensitivity of the photosensitive medium differs from a first copy to a second one.
Further, if the photosensitive medium is left unused after a copying operation, as will later be described, toner particles may sometimes fix to the area of contact between the photosensitive medium and a cleaning blade. In addition, the photosensitive medium, which is subjected to high voltage charges of varying potential, presents different surface potentials and polarities in various parts thereof and if the photosensitive medium is left in such condition, the characteristic of the drum will be adversely affected.
To overcome these problems, the photosensitive medium has been pre-treated, that is, the drum has been made to effect introductory rotation for uniform exposure prior to formation of an electrostatic latent on the photosensitive medium, whereby the sensitivity characteristic of the photosensitive medium has been made uniform for the first and subsequent copies with the fatigue effect of the photosensitive medium in view, and also the toner particles fixed to the photosensitive medium have been removed by cleaning the drum.
As a further countermeasure, the photosensitive medium has been subjected to post-treatment, that is, after substantial completion of the copying operation, the drum has been made to effect one more rotation so that accumulated charges on the photosensitive medium may be removed as by AC corona discharge.
However, the position at which the photosensitive medium stops after completion of the entire copy cycle has always been fixed and therefore, the effect of the corona charge concentrates upon one and the same portion of the photosensitive medium, which has in turn resulted in creation of wrinkled patterns on the formed image. Also, the considerable pressure under which the drum cleaner is urged against the drum has caused physical deformation of the same part of the photosensitive medium.
Thus, drawbacks are pronounced when a non-endless (non-seamless) photosensitive medium is employed. However, the adverse effect of the cleaner on the photosensitive medium may be eliminated by using a photosensitive member formed with a seam and positioning the seam adjacent to the cleaner.
On the other hand, when an endless (seamless) photosensitive medium is employed, the merit that the photosensitive medium may be started from any position thereof precludes the above-described countermeasure against the cleaner. Moreover, in the case where the copy process is controlled by a signal generated at the rotational position of the seamless drum, the stop position of the drum is periodically fixed and this prevents elimination of the said adverse effect on the photosensitive drum.
Further, such adverse effect is more pronounced as the drum is smaller in size, and there is no apparatus which has eliminated this drawback.
Also, the conventional apparatus in which the copy cycle is controlled by the rotational position of the drum has sometimes suffered from loss of scanning time depending on the copy size and this has not been effective.
Furthermore, the conventional use of microswitches, relays or the like for the control of the copy cycle, detection of jam, etc. has often led to malfunctioning and has been poor in reliability.
Still furthermore, there has been no copying apparatus of the image transfer type which is compactly designed and excellent in image formation as well as safe and reliable in operation.